1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of Related Art
A leakage current increasing with advancement of a technique for forming fine patterns in a semiconductor device is considered as a problem. The leakage current is a current flowing when the semiconductor device does not operate, and this unnecessarily leaking leakage current occupies a large proportion in a total of power consumption of the semiconductor device.
A semiconductor device is known in Japanese Patent Application Publication (JP-P2007-95787A: related art 1) in which an increase of this power consumption is suppressed by having two operation states of a standby state (a state that supply of power to a non-operation section is temporarily stopped) and a normal operation state (a state that a normal operation is performed). In the semiconductor device, the state thereof shifts from the normal operation state to the standby state by stopping the power supply to a region.
FIG. 1 is a circuit diagram of a semiconductor device 100 shown in the related art 1. Referring to FIG. 1, the semiconductor device 100 includes a controlled function block 101 and a power supply switch 102. In addition, the semiconductor device 100 includes a function block in which a control of power supply is not performed (hereinafter to be referred to as a non-controlled function block). The controlled function block 101 is a function block in which the power supply is stopped in the standby state. The power supply switch 102 connects the controlled function block 101 to a power supply wire Vdd in response to a control signal.
FIG. 2 is a layout diagram showing the semiconductor device 100 including the power supply switch 102 and the controlled function block 101. In the layout diagram of the controlled function block 101, a switch cell 107 and a function cell 108 are shown. The switch cell 107 is configured to include a first well 121. A switching transistor 113 is formed in the first well 121. In addition, the function cell 108 includes a second well 122. The first well 121 and the second well 122 are electrically isolated from each other A metal interconnection 116 is formed in a region of the first well 121. As described above, a power supply voltage VDD is supplied to the metal interconnection 116 via a first via contact (not shown).
When the power supply switch 102 is activated to connect the controlled function block 101 to the power supply line, a rush current (a current rapidly flowing in starting-up a circuit) sometimes flows in the power supply line Vddv and the power supply line Vdd. When the rush current flows, a counter electromotive force due to inductance components of a bonding wire and a long interconnection line is generated depending on a rate of change of the rush current. The counter electromotive force generates power supply noise on the power supply line, and the power supply noise continues until a power supply IC externally provided to the semiconductor device 100 responds to the rush current to sufficiently supply the power supply voltage. A malfunction of the controlled function block sometimes occurs due to the power supply noise. A technique for reducing the power supply noise by taking a countermeasure against the rush current to suppress the malfunction is known. For example, a technique is known which suppresses increase of the rush current generated in supplying the power supply by arranging a plurality of switch cells 107 and separating timings of turning on the respective switch cells.
A circuit area of the controlled function block 101 and the number of controlled function blocks 101 in the semiconductor device 100 have been increasing according to a high integration of a chip. A large controlled function block 101 and many controlled function blocks 101 cause a large rush current. In the semiconductor device 100; when the large rush current is generated, the number of the switch cells 107 is increased. However, it is very difficult to reduce the power supply noise by appropriately controlling many switch cells 107.